Apparatus and method for AAL2 packet switching on an ATM switch core

ABSTRACT

An apparatus is described having an ATM switch core, wherein the ATM switch core has an input coupled to an ingress AAL2 switch engine and an output coupled to an egress AAL2 switch engine. The ingress AAL2 switch engine has a first look-up table that can store: 1) an identification label for an AAL2 virtual channel through said ATM switch core; and, 2) an AAL2 egress connection identification label for an ingress AAL2 packet to be carried by the AAL2 virtual channel. The egress AAL2 switch engine has a second look-up table that can store an egress CID and egress VPI/VCI for the AAL2 egress connection identification label.

FIELD OF THE INVENTION

The field of invention relates generally to networking; and, morespecifically, to an apparatus and method for AAL2 packet switching on anATM switch core.

BACKGROUND

AAL2 is a packet based ATM standard (ITU-T I.366) that allows multipleusers to share the same Virtual Path Identification/Virtual ChannelInformation (VPI/VCI). FIG. 1 a elaborates on the AAL2 approach in moredetail. Within an AAL2 framework, AAL2 packets (such as the packetformed by header 101 a and payload 102 a and the packet formed by header101 b and payload 102 b) are transported over an ATM network.

As ATM cells are used to transport information over an ATM network, theAAL2 packets observed in FIG. 1 a are “broken down” into separate piecesof information that are each carried by individual ATM cells (which arenot shown in FIG. 1 a for simplicity). Upon their reception, the payloadof the ATM cells are pieced back together to form the flow of packets.

Frequently, neighboring packets are associated with differentconnections. For example, the packet formed by header 101 a and payload102 a may be destined for a first user while the packet formed by header101 b and payload 102 b may be destined for a second user. Thus, withineach header 101 a, 101 b, is a Connection Identification (CID) labelthat informs a receiving node as to which connection the correspondingpayload 102 a, 102 b belongs.

Under the current ITU-T I.366 specification, 6 bits are reserved withinthe CID which allows for 248 different connections. As such, up to 248different AAL2 connections can be carried by a single VPI/VCI ATMconnection. Note that information within different AAL2 packets may becarried by the same ATM cell. That is, the payload of a single ATM cellmay contain information at (and on either side of) the transition X fromthe first packet to the second packet seen in FIG. 1 a. As such, apointer may also be included in the packet header to signify where apacket starts and where a packet ends.

FIG. 1 b shows a model 103 for an AAL2 switch. Ingress ATM cells arereceived on a plurality of ingress lines (such as ingress line 108). Aline, such as an ingress line, may be any line that carries ATM cells(such as any OC-n line or STS-n line). The ATM cell traffic from theingress lines are collected on the ingress portion 105 a, 106 a, 107 aof one or more line cards.

The ingress portion 105 a, 106 a, 107 a of each of the line cardsreconstructs AAL2 packets from the payloads of the received ATM cells.The AAL2 packets are then forwarded to an AAL2 switch core 104 thatswitches each ingress AAL2 packet, based upon its respective CID, to theappropriate egress line card portion 105 b, 106 b, 107 b. The AAL2switch core 104 can change the CID label to an appropriate egress valuefor transmission from the switch 103. Note that, frequently, a singleline card has both an ingress portion and an egress portion.

Thus, for example, ingress portion 105 a and egress portion 105 b may beviewed as separate portions of a first line card; ingress portion 106 aand egress portion 106 b may be viewed as separate portions of a secondline card; and ingress portion 107 a and egress portion 107 b may beviewed as separate portions of a third line card. Upon receipt of anAAL2 packet at an egress portion, the AAL2 packet may be broken downinto pieces that are carried by different ATM cells which aresubsequently transmitted along the appropriate egress line (such asegress line 109).

A problem, however, is the loss of economies of scale when implementingan AAL2 switch with an AAL2 switch core 104. That is, AAL2 is a specifictype of networking approach. As other types of networking approaches arein common usage (e.g., pure ATM, AAL3/4, AAL5, Packets Over SONET (PoS),etc.), a switch having an AAL2 switch core 104 can not efficientlyswitch the traffic associated with these other types of networkingapproaches.

SUMMARY

An apparatus is described having an ATM switch core, wherein the ATMswitch core has an input coupled to an ingress AAL2 switch engine and anoutput coupled to an egress AAL2 switch engine. The ingress AAL2 switchengine has a first look-up table that can store: 1) an identificationlabel for an AAL2 virtual channel through said ATM switch core; and, 2)an AAL2 egress connection identification label for an ingress AAL2packet to be carried by the AAL2 virtual channel. The egress AAL2 switchengine has a second look-up table that can store an egress CID andegress VPI/VCI for the AAL2 egress connection identification label.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and notlimitation, in the Figures of the accompanying drawings in which:

FIG. 1 a shows a sequence of AAL2 packets;

FIG. 1 b shows a model for an AAL2 switch;

FIG. 2 shows an embodiment of an architecture that implements thefunctionality of an AAL2 switch with an ATM switch core;

FIG. 3 shows a look up table that may be used by an ingress AAL2 switchengine of FIG. 2;

FIG. 4 shows a look up table that may be used by an egress AAL2 switchengine of FIG. 2; and

FIG. 5 shows a method for implementing AAL2 switching on an ATM switchcore.

DETAILED DESCRIPTION

An apparatus is described having an ATM switch core, wherein the ATMswitch core has an input coupled to an ingress AAL2 switch engine and anoutput coupled to an egress AAL2 switch engine. The ingress AAL2 switchengine has a first look-up table that can store: 1) an identificationlabel for an AAL2 virtual channel through said ATM switch core; and, 2)an AAL2 egress connection identification label for an ingress AAL2packet to be carried by the AAL2 virtual channel. The egress AAL2 switchengine has a second look-up table that can store an egress CID andegress VPI/VCI for the AAL2 egress connection identification label.

A solution to the economy of scale problem presented in the backgroundis to implement the functionality of an AAL2 switch upon an ATM switchcore. An ATM switch core switches ATM cells based upon their VPI/VCIinformation. Various types of ATM switch core architectures exist, suchas crossbar switches and shared output buffered switches (to name just afew). As ATM cells are a fundamental transport unit for various types ofnetworking approaches (e.g., pure ATM, AAL2, AAL3/4, AAL5, PoS, etc.),an ATM switch core is better suited to cost effectively manage theswitching function of these various approaches.

FIG. 2 shows an embodiment of an architecture that implements thefunctionality of an AAL2 switch with an ATM switch core. Ingress ATMcells are received on a plurality of ingress lines (such as ingresslines 213 ₁, 213 ₂, through 213 _(x)). The ATM cell traffic from theingress lines are collected on the ingress portion 201 ₁, 201 ₂, . . .201 _(n) of one or more line cards.

Each ingress line may be deemed to correspond to an ingress port of theswitch architecture 200 of FIG. 2. In the embodiment of FIG. 2, the ATMRx units (e.g., ATM Rx unit 203) provide ATM cells that are receivedfrom a plurality of ingress ports. For example, each ATM Rx unit maycorrespond to an ATM physical layer (PHY) interface device. Those ATMcells that are not associated with an AAL2 packet flow (as identified bytheir VPI/VCI address) are forwarded to the ATM switch core 204 (e.g.,along logical path 205 for cells provided by ATM Rx unit 203).

Those ATM cells having a VPI/VCI associated with an AAL2 packet flow areforwarded to an ingress AAL2 switch engine 206. An AAL2 ingress switchengine 206, as described in the exemplary details that follow, is afunctional unit that effectively converts information that characterizesan ingress AAL2 packet (e.g., its CID value, its VPI/VCI address, itsingress port, etc.) into: 1) information that is used by the ATM switchcore 204 to direct the AAL2 packet to its appropriate egress line cardportion; and 2) information that is used by the appropriate egress linecard portion to understand which egress port, egress CID value andegress VPI/VCI information should be implemented into the outgoing AAL2packet and the outgoing ATM cells used to transport it.

In the embodiment of FIG. 2, the AAL2 switch engine 206 reassembles thepayloads from the ATM cells it receives. Note that those ATM cellshaving the same VPI/VCI can correspond to a multi-user stream of AAL2packets such as the stream of packets shown back in FIG. 1 a. As asingle ingress port may support multiple VPI/VCI addresses that eachsupport an AAL2 packet stream; and, as multiple ingress ports may bereceived by the ATM Rx unit 203, a plurality of AAL2 packet streams maybe processed by the ingress AAL2 switch engine 206 of FIG. 2.

The switch engine 206 effectively directs each AAL2 packet, regardlessas to which AAL2 packet stream it arrived on, to its appropriate egressline card portion (e.g., egress line portion 202 ₁, 202 ₂, . . . or 202_(n) as seen in FIG. 2) through the ATM switch core 204. FIG. 3 shows anexemplary look-up table 300 that may be employed by an ingress AAL2switch engine 206 to help direct a particular AAL2 packet to itsappropriate egress line card portion.

The inputs to the look-up table 300 of FIG. 3 include: 1) the CID of theAAL2 packet to be directed; 2) the VPI/VCI address of the AAL2 packetstream that the AAL2 packet to be directed arrived with; and 3) the porton which the AAL2 packet arrived. The combination of these three itemsare unique to any AAL2 packet arriving at the ATM Rx unit 203 for aparticular user. That is, for example, CID values may be reused fordifferent connections across the various VPI/VCI address values thatcorrespond to an AAL2 packet stream. In the embodiment of FIG. 3,VPI/VCI values may conceivably also be reused for different AAL2 streamsacross the various input ports that are received by the ATM Rx unit 203.

Thus, in the embodiment of FIG. 3, each input/output entry of the lookup table 300 corresponds to a particular AAL2 connection supported bythe switch 200 of FIG. 2. As seen in the embodiment of FIG. 3, theoutput contents of the look up table 300 provide: 1) The pipe number(P#); and 2) the egress identification number (EID). The P# isinformation that is used by the ATM switch core 204 to direct the AAL2packet to its appropriate egress line card portion.

The EID information (which is appended to the payload of the AAL2 packetas it traverses the ATM switch core 204) is transported with the payloadof a received AAL2 packet as it traverses the ATM switch core 206. TheEID information helps the appropriate egress line card portionunderstand which egress port, egress CID value and egress VPI/VCIinformation should be implemented into the outgoing AAL2 packet and theoutgoing ATM cells used to transport it. In the following, a discussionof the P# will precede a discussion of the EID.

In the embodiment of FIGS. 2 and 3, the P# effectively points to (orotherwise triggers the use of) a local, virtual channel within the ATMswitch core 204 used to carry AAL2 packet flows. Exemplary AAL2 virtualchannels 208 ₁, 208 ₂, 208 _(n) that respectively couple ingress linecard portion 201 _(n) to each egress line card portion 202 ₁, 202 ₂ . .. 202 _(n) are shown in FIG. 2. The AAL2 virtual channels 208 ₁, 208 ₂,208 _(n) may be established within the ATM switch core 204 as permanentconnections in light of the AAL2 packet flows that the switch 200 isconfigured to support.

For example in one approach, if an ingress line card portion isconfigured to actively receive AAL2 packet flows (e.g., by enabling theingress switch AAL2 engine), an AAL2 virtual channel is establishedthrough the ATM switch core 204 from the ingress line card to eachegress line card portion 202 ₁, 202 ₂ through 202 _(n). For example, asseen in FIG. 2, once ingress line card portion 201 _(n) is configured toactively receive an AAL2 packet flow, AAL2 virtual channels 208 ₁, 208₂, 208 _(n) are created within the ATM switch core 204 in response. Notethat from the perspective of the ATM switch core 204, each AAL2 virtualchannel 208 ₁, 208 ₂, 208 _(n) may be viewed as an ATM virtual channel.

This provides the newly configured AAL2 service with the versatility toswitch AAL2 packets to any egress destination. In an alternateembodiment, the egress line of a particular AAL2 packet connection isfixed. As such, only one virtual channel that connects the ingress linecard portion to the appropriate egress line card portion is needed.

In a further embodiment of either of these approaches, the capacity ofthe virtual channel through the ATM switch core 204 is extended tosupport more than one AAL2 packet flow (e.g., up to 248 different AAL2connections). This allows an ingress line card portion that manages thereception of different AAL2 packet connections (e.g., if ingress linecard portion 201 _(n) is configured to manage different AAL2 connectionsreceived across ingress lines 213 ₁ through 213 _(n)) to “pipe” AAL2packets having the same egress line card portion destination (e.g.,egress line card portion 202 ₁) over a common virtual channel throughthe ATM switch core (e.g., virtual channel 208 ₁). For example, undercurrent implementations, each VPI/VCI recognized by the ATM switch core204 can have as many as 248 connections via the CID header parameter.

As discussed, non AAL2 packet flows (such as pure ATM cell switchingflows) avoid the ingress AAL2 switch engine 206 and are presented to theATM switch core 204 and switched by normal means. For example, for pureATM flows on ingress line card portion 201 _(n), ATM cells traverselogical path 205 and are presented to the ATM switch core 204. The ATMswitch core 204 may switch these cells based upon their VPI/VCIinformation.

AAL2 packets are also effectively presented to the ATM switch core 204after processing by the ingress AAL2 switch engine 206. In anembodiment, AAL2 packet payloads destined for the same egress line cardportion are inserted into one or more ATM cells having a VPI/VCI addressthat corresponds to the appropriate virtual channel (e.g., AAL2 virtualchannel 208 ₁ for egress line card portion 202 ₁, AAL2 virtual channel208 ₂ for egress line card portion 202 ₂, and AAL2 virtual channel 208_(n) for egress line card portion 202 _(n)). In this approach, thisVPI/VCI address corresponds to the P# that is listed in the ingress AAL2switching engine look up table 300 shown in FIG. 3.

As such, the P# effectively points to the appropriate AAL2 virtualchannel and also provides a means (e.g., a VPI/VCI address) that isrecognized by an ATM switch core 204 to appropriately direct trafficthrough the switch core 204. Note that the stream of ATM cells carryingAAL2 packet payload information across the same virtual channel (throughthe ATM switch core 204) may be formatted with appropriate AAL2overhead. As such, a stream of AAL2 packets (similar to that shown inFIG. 1 a) are reassembled from the cell payloads upon their reception atthe destination egress line card portion.

In this approach, the cells used to carry the AAL2 packet stream areformatted with the VPI/VCI found as the P# within look up table 300 ofFIG. 3. In this case, the egress AAL2 switch engine (e.g., egress AAL2switch engine 210 for destination line card portion 202 ₁) performs theappropriate AAL2 packet reassembly. Note that, upon the reception of ATMcells from the ATM switch core 204 at an egress line card portion, thoseATM cells having a VPI/VCI address that corresponds to an AAL2 virtualchannel through the ATM switch core 204 are diverted for processing bythe egress AAL2 switching engine 210. That is, as virtual channels carryAAL2 information, the egress AAL2 switching engine 210 is invoked forcells carried along these channels.

Those ATM cells not having a VPI/VCI address that corresponds to an AAL2virtual channel through the ATM switch core 204 follow logical path 211to the ATM Tx unit 212. Note that, these “non AAL2” cells may have theirVPI/VCI address changed by the ATM switch core 204 consistent with ATMcell switching technology. For those cells having a VPI/VCI address thatcorresponds to an AAL2 virtual channel through the ATM switch core 204,however, no such change is necessary as the virtual channel may beviewed as local to the ATM switch core 204.

Recall that the EID information found in the look-up table 300 of Figureis effectively appended to the payload of an AAL2 packet as it traversesthe ATM switch core 204. The EID, as described in more detailimmediately below, helps the appropriate egress AAL2 switch engine 210understand which egress port, egress CID value and egress VPI/VCIinformation should be implemented into the outgoing AAL2 packets and theoutgoing ATM cells used to transport them.

The EID may be viewed as a local extension to the CID. That is, recallthat the CID identifies AAL2 connections that are particular to aVPI/VCI. In the embodiment of FIG. 2, the EID identifies AAL2connections that are particular to an egress line card portion. That is,each egress line card portion 202 ₁, 202 ₂, . . . 202 _(n) “keeps trackof” separate EID numbers that are used to identify each AAL2 connectionthat it controls the transmission of.

Thus, for example, when updating the look up table 300 for an ingressswitch engine (e.g., ingress switch engine 206) with information for anew connection, the particular EID number given to the connection isdetermined in light of the available EID numbers that may be used by theparticular egress switch engine (e.g., egress switch engine 210) thatwill handle the traffic for the connection. In order for the switch tohandle more than one VPI/VCI address worth of AAL2 traffic per egressline card portion (i.e., in order for the switch to handle more than 248outgoing AAL2 connections per egress line card portion), the size of theEID field should be larger than the size of the CID field.

In an embodiment, the EID field size is 16 bits which allows for over64,000 AAL2 connections per egress line card portion. Alternateembodiments may reduce the EID field size to less than 16 bits (if lessthan 64,000 AAL2 connections per egress line card portion is desired) ormay expand the EID field size to more than 16 bits (if more than 64,000AAL2 connections per egress line card portion is desired). Varioustechniques may be used to append the EID number to an AAL2 packet priorto processing by the ATM switch core. For example, in an embodimentwhere a stream of AAL2 packets (similar to FIG. 1 a) are segmented andcarried by ATM cells 204 over the ATM switch core, the EID may becomprised of the CID field plus additional header space within the AAL2packet (e.g., reserved bit locations).

Alternatively or in combination, the ATM switch core interface 207 mayallow for a control header that is presented along with each celloffered to the ATM switch core 204 for service. Such a control headermay be formatted to include the EID number particular to the AAL2packet(s) being carried by the ATM cell. Such a control header may alsobe used to identify an AAL2 virtual channel number (i.e., a P# otherthan a VPI/VCI address) that is recognized by the ATM switch core 204.

After the payload for an AAL2 packet and its corresponding EID number isrecognized by an egress AAL2 switch engine 210, the egress AAL2 switchengine 210 looks up appropriate information for the outgoing connectionbased upon the EID number. FIG. 4 shows an embodiment of such a look uptable 400. As mentioned just above, the look up is based upon the EIDnumber. As such, the EID number is the look up table 400 inputparameter.

The output parameters in the look up table embodiment 400 of FIG. 4include: 1) the CID number for the outgoing connection; 2) the VPI/VCIaddress to be used by the ATM cells that will be used to transport theoutgoing AAL2 packet; and 3) the outgoing port (e.g., outgoing networkline such as any of lines 214 ₁, 214 ₂, through 214 _(y)). Note that,consistent with the operation of an AAL2 switch, CID numbers areswitched from ingress to egress as discussed with respect to FIG. 1 b.Furthermore, as is clear from above, an egress AAL2 switch engineeffectively converts the EID into information that is used to properlytransmit the AAL2 packet (e.g., its CID, its corresponding VPI/VCI andits corresponding output port).

Once the information is gathered for the outgoing connection from thelook-up table, the proper AAL2 header structure is formed (including theCID found in the table 400) and appended to the payload. The AAL2 headerand payload is then segmented as necessary into ATM cells having theVPI/VCI found in the table. These cells are then forwarded to the ATM Txunit (such as ATM Tx unit 212) with the outgoing port information foundin the look up table so that the cells are transported over the correctoutgoing line. The ATM Tx unit 212 may correspond to an ATM transmissionPHY device.

FIG. 5 shows a methodology that reviews the AAL2 switching sequenceapproach discussed above. Note that, although the methodology of FIG. 5is written to correspond to Common Part Sublayer (CPS) AAL2 packets,other types of AAL2 packet characterizations (such as Service SpecificConvergence Sublayer (SSCS)) also apply to the methodology of FIG. 5.

Upon the reception of ATM cells that carry AAL2 packet information, theingress AAL2 packet payload is tagged 501 with an egress identificationlabel (e.g., the EID discussed above). The ingress AAL2 packet payloadand egress identification label are then formatted 502 for switching byan ATM switch core (e.g., by incorporating the payload as part of anAAL2 packet stream (that includes the EID in its header space) which isfurther segmented or otherwise incorporated into a series of ATM cells).

The ingress AAL2 packet payload and its corresponding EID are thenswitched 503 by the ATM core to the appropriate egress line cardportion. The EID is then used at the egress line card to identify 504the CID and VPI/VCI information for the outgoing connection the AAL2payload is to be delivered over. Note that the ingress or egress AAL2switch engines may be implemented as a processor that performs themethodologies described above in software, as dedicated logic thatperforms the methodologies described above, or as some combination ofboth.

Thus, embodiments of the present description may be implemented not onlywithin a semiconductor chip but also within machine readable media. Forexample, the designs discussed above may be stored upon and/or embeddedwithin machine readable media associated with a design tool used fordesigning semiconductor devices. Examples include a netlist formatted inthe VHSIC Hardware Description Language (VHDL) language, Veriloglanguage or SPICE language. Some netlist examples include: a behavioriallevel netlist, a register transfer level (RTL) netlist, a gate levelnetlist and a transistor level netlist. Machine readable media alsoinclude media having layout information such as a GDS-II file.Furthermore, netlist files or other machine readable media forsemiconductor chip design may be used in a simulation environment toperform the methods of the teachings described above.

Thus, it is also to be understood that embodiments of this invention maybe used as or to support a software program executed upon some form ofprocessing core (such as the CPU of a computer) or otherwise implementedor realized upon or within a machine readable medium. A machine readablemedium includes any mechanism for storing or transmitting information ina form readable by a machine (e.g., a computer). For example, a machinereadable medium includes read only memory (ROM); random access memory(RAM); magnetic disk storage media; optical storage media; flash memorydevices; electrical, optical, acoustical or other form of propagatedsignals (e.g., carrier waves, infrared signals, digital signals, etc.);etc.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

1. An apparatus, comprising: an ATM switch core having an input coupledto an ingress AAL2 switch engine and an output coupled to an egress AAL2switch engine, said ingress AAL2 switch engine having a first look-uptable that can store: 1) an identification label for establishing alocal AAL2 virtual channel through said ATM switch core, and 2) an AAL2egress connection identification label (EID) for an ingress AAL2 packetto be carried by said AAL2 virtual channel, said egress AAL2 switchengine having a second look-up table that can store the EID, and anegress port number, an egress CID, and an egress VPI/VCI associated withthe EID, said egress AAL2 switch engine replaces parts of the ingressAAL2 packet with the egress CID and the egress VPI/VCI, producing anoutgoing AAL2 packet.
 2. The apparatus of claim 1 wherein said firstlook-up table can store input look-up information that comprises aningress CID of said ingress AAL2 packet.
 3. The apparatus of claim 2wherein said input look-up information further comprises a VPI/VCI of anATM cell that carries said ingress AAL2 packet.
 4. The apparatus ofclaim 2 wherein said input look-up information further comprises aningress port number of an ATM cell that carries said AAL2 packet.
 5. Theapparatus of claim 1 further comprising an ATM physical layer devicecoupled to an input of said ingress AAL2 switch engine, said ATMphysical layer device for providing ATM cells received from one or moreingress network lines.
 6. The apparatus of claim 5 wherein at least oneof said one or more ingress network lines is an OC-n based network line.7. The apparatus of claim 1 further comprising an ATM physical layerdevice coupled to an output of said egress AAL2 switch engine, said ATMphysical layer device for transmitting ATM cells over one or more egressnetwork lines.
 8. The apparatus of claim 7 wherein at least one of saidone or more egress network lines is an OC-n based network line.
 9. Theapparatus of claim 1 wherein at least one of said switch engines atleast partially comprises a processor that runs software.
 10. Theapparatus of claim 1 wherein said AAL2 packet further comprises a CPSAAL2 packet.
 11. The apparatus of claim 1 wherein said AAL2 packetfurther comprises a SSCS AAL2 packet.
 12. A method, comprising: a)producing an AAL2 virtual channel pipe number and an AAL2 egressconnection identification label EID) in response to an ingress AAL2packet CID and VPI/VCI; b) forwarding at least said ingress AAL2 packetpayload and said AAL2 egress connection identification label (EID) overa local AAL2 virtual channel established within an ATM switch core, saidAAL2 virtual channel identified by said AAL2 virtual channel pipenumber; c) replacing the ingress AAL2 packet CID and VPI/VCI by anegress AAL2 switch engine; and d) producing an egress AAL2 packetincluding an egress CID and an egress VPI/VCI based on said AAL2 egressconnection identification label, said egress AAL2 packet carrying saidingress AAL2 packet payload.
 13. The method of claim 12 furthercomprising reassembling ingress ATM cells into said ingress AAL2 packet.14. The method of claim 13 further comprising receiving said ingress ATMcells from a network line.
 15. The method of claim 14 wherein saidnetwork line is an OC-n based network line.
 16. The method of claim 12wherein said producing an AAL2 virtual channel pipe number and an AAL2egress connection label further comprises performing a lookup based uponsaid ingress packet CID and VPI/VCI.
 17. The method of claim 12 whereinsaid producing an egress AAL2 packet CID and VPI/VCI further comprisesperforming a lookup based upon said AAL2 egress connectionidentification label.
 18. The method of claim 12 further comprisingsegmenting said egress AAL2 packet into egress ATM cells, said egressATM cells having said egress packet VPI/VCI.
 19. The method of claim 18further comprising transmitting said egress ATM cells over an egressnetwork line.
 20. The method of claim 19 wherein said network line is anOC-n based network line.
 21. The method of claim 12 wherein either saidingress AAL2 packet or said egress AAL2 packet is a CPS AAL2 packet. 22.The method of claim 12 wherein either said ingress AAL2 packet or saidegress AAL2 packet is a SSCS AAL2 packet.
 23. An apparatus, comprising:a) means for producing an AAL2 virtual channel identification label andan AAL2 egress connection identification label in response to an ingressAAL2 packet CID and VPI/VCI; b) means for forwarding at least saidingress AAL2 packet payload and said AAL2 egress connectionidentification label over a local AAL2 virtual channel establishedwithin an ATM switch core, said AAL2 virtual channel identified by saidAAL2 virtual channel identification label; c) means for replacing theingress AAL2 packet CID and VPI/VCI by an egress AAL2 switch engine; andd) mean producing an egress AAL2 packet including an egress CID and anegress VPI/VCI based on said AAL2 egress connection identificationlabel, said egress AAL2 packet carrying said ingress AAL2 packetpayload.
 24. The apparatus of claim 23 further comprising means forreassembling ingress ATM cells into said ingress AAL2 packet.
 25. Theapparatus of claim 24 further comprising means for receiving saidingress ATM cells from a network line.
 26. The apparatus of claim 25wherein said network line is an OC-n based network line.
 27. Theapparatus of claim 23 further comprising means for segmenting saidegress AAL2 packet into egress ATM cells, said egress ATM cells havingsaid egress packet VPI/VCI.
 28. The apparatus of claim 27 furthercomprising means for transmitting said egress ATM cells over an egressnetwork line.
 29. The apparatus of claim 28 wherein said network line isan OC-n based network line.
 30. The apparatus of claim 23 wherein eithersaid ingress AAL2 packet or said egress AAL2 packet is a CPS AAL2packet.
 31. The apparatus of claim 23 wherein either said ingress AAL2packet or said egress AAL2 packet is a SSCS AAL2 packet.
 32. A machinereadable medium having stored thereon sequences of instructions, which,when executed by a digital processing system cause said digitalprocessing system to perform a method, said method comprising: producingan AAL2 virtual channel identification label and an AAL2 egressconnection identification label in response to an ingress AAL2 packetCID and VCI/VPI so that at least said ingress AAL2 packet payload andsaid ML2 egress connection identification label can be forwarded over alocal ML2 virtual channel established within an ATM switch core, saidAAL2 virtual channel identified by said AAL2 virtual channelidentification label; replacing an ingress AAL2 packet with an egressCID and an egress VPI/VCI; producing an egress AAL2 packet based on thereplacement in response to an AAL2 egress connection identificationlabel, at an egress switch engine, said AAL2 egress connectionidentification label associated forwarded over an ATM switch core withat least a portion of an AAL2 packet payload, said egress AAL2 packetcarrying said ingress AAL2 packet payload.